My golden was about 10 or 11 when she started doing that. It's no concern unless there are wounds. Mine did it because she had bad arthritis and I guess it was as close to a foot massage as she could get.
your dog might have skin allergies or an infection. talk to your vet for information
My dog has done that too. For now I just keep an eye on the spot, but previously the Vet asked for her to wear a protective attachment to her collar. She is 10 years now, and she looks content when she licks this spot on her foot.